1. Field of the Invention:
The present invention relates to a method of and an apparatus for limiting electrical loads due to electrical equipment mounted on an electric vehicle, and more particularly to a method of and an apparatus for enabling electrical loads due to electrical equipment mounted on an electric vehicle to be restricted based on a relationship between a desired attainable travel distance and the depth of discharge of a battery.
2. Description of the Related Art:
A large battery, which has heretofore been developed, should be mounted on an electric vehicle in order to increase a running range or distance. Therefore, the weight of the battery increases.
It is however desirable that the battery is reduced in weight in the electric vehicle which is to cover a desired distance with less electrical energy. Under the existing circumstances, the capacity of the battery is inevitably limited. There is therefore a demand for a technique of automatically limiting electrical loads imposed by electrical equipment or components mounted on the vehicle in order to maximize the running distance at one charge level.
In the latest vehicle, the kind and number of electrical equipment increases and hence loads connected to a battery become greater. Therefore, various techniques for limiting the loads have been developed. Conventional examples, which will be described below, are not related to the electric vehicle, but the following disclosure will be described as examples. A technique for reducing current flowing through a fan motor when the voltage of a battery is reduced, has been disclosed in Japanese Utility Model Application Laid-Open Publication No. 56-30524. Another technique for melting a fuse to electrically disconnect an electrical load from a battery when the voltage of the battery is reduced to a prescribed level or below, has been disclosed in Japanese Utility Model Application Laid-Open Publication No. 57-53702. A further technique for cutting off or disconnecting an electrical load from a battery when the battery is in an over-discharged state, has been disclosed in Japanese Patent Application Laid-Open Publication No. 62-241733. A still further technique for cutting off the supply of electric power to some of the electrical loads when the voltage of a battery is reduced, has been disclosed in Japanese Patent Application Laid-Open Publication No. 63-255152. A still further technique for cutting off the supply of electric power to an electrical load when the voltage of a battery is reduced to a given value or below and producing a warning, has been disclosed in Japanese Patent Application Laid-Open Publication No. 63-284052. A still further technique for varying a supply voltage depending on the state of operation of an engine has been disclosed in Japanese Utility Model Application Laid-Open Publication No. 63-61360. A still further technique for reducing the torque output of the motor as a result of a detected malfunction in the battery system, such as for a zinc-bromine battery that requires fluid circulation by a pump and precise temperature control, has been disclosed in Japanese Patent Application Laid-Open Publication No. 63-77302.
In all the techniques referred to above, however, the electrical loads are limited only under a certain restriction mode. Therefore, the running distance may or may not increase to a driver's desired arrival point even if such techniques are applied to the electric vehicle. There is also a situation in which the electrical loads are occasionally limited beyond need. Owing to such a restriction, functions inherent to the electric vehicle cannot be achieved and the running condition desired by the driver cannot be obtained.